Grammar experts: "Should" as conjunction?

Posted by Rob F on January 02, 2004

In listing the definitions of "should", the online dictionaries fail to mention that it can be used as a conjunction (specifically a subordinating conjunction). For example, consider the following sentence:
"Should time permit, the audience will be invited to ask questions."

One can substitute "If time permits" for "Should time permit" without changing the meaning. "If", when used in this context, is a subordinating conjunction. Wouldn't that make "Should" a subordinating conjunction too?

Is this a rare oversight by the dictionary publishers, or is this use of "Should" somehow grammatically incorrect?